Two important considerations:
Heavy doping of both p and n sides.
Appropriate "break down voltage‟ under reverse bias.
Circuit diagram:

Principle: Even small reverse bias voltage (5V) can produce a very high electric field because the depletion region is very thin.
Working: The unregulated DC voltage is connected to the Zener diode through a series resistance RS such that the Zener diode is reverse biased. In breakdown region, the Zener voltage remains constant even though the current through Zener diode changes. This helps to regulate the output voltage.